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SV Skalliwag #141
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The Pressure Relief Valve on my Water Heater has been removed and is awaiting replacement. The water heater is partially empty. Can I run the engine with the water heater half empty? The engine collant hose goes into and out of the water heater to heat the water while the engine runs.
 

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One of None
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The relief valve is a big box store item, easy to get! Water under pressure will boil very easily, even though I don't think it would hurt the Heat Exchanger DO NOT use a pipe plug in the hole.
 

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You have no bypass or isolation valves? What happens if you run out of water when you are on a trip? Or if you get a leak in the heater?
 

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The easiest thing to do is just cut off the flow of engine coolant to the hot water tank via the isolation valve. I would think you would have such a valve, but if not I do not believe that any harm will come to the heat exchanger in the hot water tank if the tank is low on water. That would not however be true for the electrical element in the hot water tank should the tank be empty of water. Just don't plug the tank into an electrical connection until you get a proper relief valve and fill the tank with water.
 

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The engine coolant circulates in a HX which is sealed off from the water heater. You do not need water in the heater to run the engine. The "coil" will just get to engine temp and heat the empty space in the water heater like a radiator....

Looks like this:
 

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Load Bearing Member
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Thanks again for great info, Maine Sail.

My new boat has the same sort of system and the loop to the water heater runs in parallel with the engine heat exchanger.

I asked the surveyor about the possibility of losing coolant through a failure of this new loop. I'd hate to think that my 'nice to have' hot water heater would ever cause a failure of my 'must have'* engine.

His feeling was that the unit sees only coolant and fresh water and that corrosion/failure was unlikely. I agree (what do I know?), but would feel better if there were valves to isolate the extra loop. There are none.

Are isolation valves commonly installed on a system like this?

I plan to keep a few threaded pipe 'plugs' of the proper size on board to blank off the loop if it were to fail. I could then refill the coolant from on board water and make it home. Right?







*Debatable, I know, but not in this thread. :rolleyes:
 

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SV Skalliwag #141
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744 Posts
Discussion Starter #7
Thanks Mainsail! I feel much better now taking the boat out for her 2014 shakedown.n cruise while I wait for the RV to arrive.
 

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CarbonSink: It would be easy to add valves to stop the flow of coolant through the heater. On my Yanmar 2GM20F the coolant lines to the water heater were obvious (at the top of the engine) and easy to access.

I will say that one of the best things that I did to my boat was removing the heater. It took up a lot of useful space, I never used the hot water out of it, and it added a lot of dead weight and water that I couldn't access. So my suggestion would be to live with it for one season unchanged, keep track of how often you use it, then decide if you really want it.
 

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Load Bearing Member
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Thanks Alex, but the Admiral swooned when she heard, "pressure water, hot & cold" so that might not be a viable option.

It does take up some space.
 

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We thought it was cool during the purchase period and inspection as well. After cruising for half a summer my wife had forgotten that we ever had hot water, when I mentioned removing it she said "oh, I forgot that we had it".

Since it only works after medium to long periods of motoring or when on shore power it almost never had any value for us.
 

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All the installation manuals for heaters state that the connections to your engine are ciritical, 'cuz if they leak you'll lose your coolant!

Hot water heater hose replacement
UNDER THE GALLEY SOLE

If your hoses wear out, you lose ALL engine coolant, and your engine will pack it in. Really!!!

Hose replacement to HW heater w/ Hose Flix
 
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